[英]Transpose DataFrame single row to column in Spark with scala
我在这里看到了这个问题: Transpose DataFrame without Aggregation in Spark with scala而我想做的恰恰相反。
我有一个单行的 Dataframe,其值为字符串、整数、布尔值、数组:
+-----+-------+-----+------+-----+
|col1 | col2 |col3 | col4 |col5 |
+-----+-------+-----+------+-----+
|val1 | val2 |val3 | val4 |val5 |
+-----+-------+-----+------+-----+
我想像这样转置它:
+-----------+-------+
|Columns | values|
+-----------+-------+
|col1 | val1 |
|col2 | val2 |
|col3 | val3 |
|col4 | val4 |
|col5 | val5 |
+-----------+-------+
我正在使用 Apache Spark 2.4.3 和 Scala 2.11
编辑:值可以是任何类型(int、double、bool、array),而不仅仅是字符串。
从Spark-2.4
使用arrays_zip
和array(column_values), array(column_names)
然后分解得到结果。
Example:
val df=Seq((("val1"),("val2"),("val3"),("val4"),("val5"))).toDF("col1","col2","col3","col4","col5")
val cols=df.columns.map(x => col(s"${x}"))
val str_cols=df.columns.mkString(",")
df.withColumn("new",explode(arrays_zip(array(cols:_*),split(lit(str_cols),",")))).
select("new.*").
toDF("values","Columns").
show()
//+------+-------+
//|values|Columns|
//+------+-------+
//| val1| col1|
//| val2| col2|
//| val3| col3|
//| val4| col4|
//| val5| col5|
//+------+-------+
UPDATE:
val df=Seq(((2),(3),(true),(2.4),("val"))).toDF("col1","col2","col3","col4","col5")
df.printSchema
//root
// |-- col1: integer (nullable = false)
// |-- col2: integer (nullable = false)
// |-- col3: boolean (nullable = false)
// |-- col4: double (nullable = false)
// |-- col5: string (nullable = true)
//cast to string
val cols=df.columns.map(x => col(s"${x}").cast("string").alias(s"${x}"))
val str_cols=df.columns.mkString(",")
df.withColumn("new",explode(arrays_zip(array(cols:_*),split(lit(str_cols),",")))).
select("new.*").
toDF("values","Columns").
show()
//+------+-------+
//|values|Columns|
//+------+-------+
//| 2| col1|
//| 3| col2|
//| true| col3|
//| 2.4| col4|
//| val| col5|
//+------+-------+
不使用arrays_zip
(在=> Spark 2.4中可用)的想法有所不同]并得到以下...
它将以更简单的方式map
flatmap
explode
功能)...
此处map
function(用于列)创建一个新的 map 列。 输入列必须分组为键值对。
import org.apache.spark.sql.functions._
val df: DataFrame =Seq((("val1"),("val2"),("val3"),("val4"),("val5"))).toDF("col1","col2","col3","col4","col5")
var columnsAndValues = df.columns.flatMap { c => Array(lit(c), col(c)) }
df.printSchema()
df.withColumn("myMap", map(columnsAndValues:_*)).select(explode($"myMap"))
.toDF("Columns","Values").show(false)
结果:
root
|-- col1: string (nullable = true)
|-- col2: string (nullable = true)
|-- col3: string (nullable = true)
|-- col4: string (nullable = true)
|-- col5: string (nullable = true)
+-------+------+
|Columns|Values|
+-------+------+
|col1 |val1 |
|col2 |val2 |
|col3 |val3 |
|col4 |val4 |
|col5 |val5 |
+-------+------+
如果您有不同的类型将它们转换为字符串...其余步骤不会改变..
val df1 = df.select(df.columns.map(c => col(c).cast(StringType)): _*)
完整示例:
import org.apache.spark.sql.functions._
import spark.implicits._
import org.apache.spark.sql.Column
val df = Seq(((2), (3), (true), (2.4), ("val"))).toDF("col1", "col2", "col3", "col4", "col5")
df.printSchema()
/**
* convert all columns to to string type since its needed further
*/
val df1 = df.select(df.columns.map(c => col(c).cast(StringType)): _*)
df1.printSchema()
var ColumnsAndValues: Array[Column] = df.columns.flatMap { c => {
Array(lit(c), col(c))
}
}
df1.withColumn("myMap", map(ColumnsAndValues: _*))
.select(explode($"myMap"))
.toDF("Columns", "Values")
.show(false)
结果:
root
|-- col1: integer (nullable = false)
|-- col2: integer (nullable = false)
|-- col3: boolean (nullable = false)
|-- col4: double (nullable = false)
|-- col5: string (nullable = true)
root
|-- col1: string (nullable = false)
|-- col2: string (nullable = false)
|-- col3: string (nullable = false)
|-- col4: string (nullable = false)
|-- col5: string (nullable = true)
+-------+------+
|Columns|Values|
+-------+------+
|col1 |2 |
|col2 |3 |
|col3 |true |
|col4 |2.4 |
|col5 |val |
+-------+------+
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